1. Field of the Inventions
The present inventions relate to control systems, and more specifically to control systems for use with positive displacement pumps.
2. Description of the Related Art
Positive displacement pumps, such as metering pumps, can be used to pump liquids at adjustable flow rates which are precise when averaged over time. Metering pumps include diaphragm metering pumps, peristaltic metering pumps, piston pumps, etc. A peristaltic roller pump typically has three or more rollers, but may have other configurations. The rollers are generally spaced circumferentially evenly apart and are generally mounted on a rotating carrier that moves the rollers in a circle. A length of flexible tubing is typically placed between the rollers and a semi-circular wall. In medical applications, the tubing can be a relatively soft and pliable rubber tubing. For relatively high pressure industrial applications, however, the tubing can be exceedingly durable and rigid, albeit flexible under the high pressure of the rollers.
In use, the rollers rotate in a circular movement and compress the tubing against the wall, squeezing the fluid through the tubing ahead of the rollers. The rollers are configured to almost completely occlude the tubing, and operate essentially as a positive displacement pump, each passage of a roller through the semicircle pumps the entire volume of the fluid contained in the tubing segment between the rollers.
As a positive displacement pump, relatively high positive pressures (e.g., up to 125 psi) can be generated at the pump outlet. Peristaltic roller pumps are typically driven by a constant speed motor that draws fluid at a substantially constant rate.